1. Field of the Invention
This invention relates to the structure of an optical disc having an auxiliary information recording area.
The present application claims priority from Japanese Application No. 2005-295203, the disclosure of which is incorporated herein by reference.
2. Description of the Related Art
FIG. 1 illustrates the structure of a conventional optical disc containing an auxiliary information recording area, such as DVD.
The optical disc D shown in FIG. 1 has a record surface containing a main information recording area DA, a control information recording area DB provided next to the inner peripheral end of the main information recording area DA, and an auxiliary information recording area DC provided next to the inner peripheral end of the control information recording area DB.
In the auxiliary information recording area DC which is what is called BCA (Burst Cutting Area), marks M are written in barcode form for identifying information such as an ID number for identifying the individual optical discs D, at the factory prior to shipment.
The identifying information written in the auxiliary information recording area (BCA) DC is read when the mark M is detected by a pickup for recording/reproducing main information in/from the main information recording area DA and control information in/from the control information recording area DB.
Recently, the proposition that the identifying information such as an ID number recorded in the auxiliary information recording area (BCA) DC is used as a copy protection key has been made.
FIG. 2 is a partially enlarged diagram illustrating the record surface of the auxiliary information recording area (BCA) DC of the optical disc D.
In FIG. 2, each of the marks M in barcode form representing the identifying information extends in the radial direction of the optical disc D.
Track grooves G extend in the circumferential direction in the auxiliary information recording area (BCA) DC as well as in the main information recording area DA and the control information recording area DB.
Problems possibly arising in conventional optical discs D structured as described above will be described below.
The track groove G formed in the auxiliary information recording area (BCA) DC of the conventional optical disc D is relatively deep as in the case of the main information recording area DA and the control information recording area DB. Therefore, when the identifying information is read under open tracking conditions from the auxiliary information recording area (BCA) DC, the interference between return light of the laser beam from the track groove G and the land between the track grooves G is increased. The increased interference affects a RF signal reproduced from the auxiliary information recording area (BCA) DC. As a result, the reading of the identifying information recorded in the auxiliary information recording area (BCA) DC may be made impossible.
FIG. 3 illustrates the reproduced signal waveform of the RF signal read from the auxiliary information recording area (BCA) DC in the conventional optical disc D.
As shown in FIG. 3, in the portion A in which the interference is caused by the track groove G, if, for example, a set slice level L is 50%, the occurrence of a portion B in which a RF signal from the auxiliary information recording area (BCA) DC cannot be detected results.
In this event, the identifying information recorded in the auxiliary information recording area (BCA) DC may possibly fail to function as a copy protect key with reliability.